On Nov 9, 2010, at 7:12 AM, Z.Xiao wrote:
Dear all gmxers,
I meet some problems when I use the tabulated bonded potential.
My original function is a sum of An*cos(x)^n (n=1-8).For short here
I replaced it by cos(x).
if f(x)=cos(x),then -f'(x)=sin(x).and the numberical derivative -
f'(x)=-(y(n+1)-y(n-1))/2.
here you should have dy/dx, re you really doing this?
but there are great discrepancy between the two -f'(x).
which is right?
and if mdrun with the derivative of original function I would met a
warning:the forces deviate
on average 207% from minus the numerical derivative of the
potential.but mdrun with the the
numberical derivative there is no warning.
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